I encountered a miscompilation case with zbs, where bseti without sign
extension emitted from bsetidisi pattern leads to wrong output.

Take pr68648.c as an example, -march=rv64gc_zba_zbb_zbs -O3 did not generate
sext.w in int bar (void) and led to a wrong value in a0. It seems that the
partial subreg
check is wrongly set to the immediate operand.

int foo (void):
    li  a0,123
    ret
int bar (void):
    addi    sp,sp,-16
    sd  ra,8(sp)
    call    foo         # a0 123
    li  a5,248639488    # a0 123, a5 0xed1f000
    addi    a5,a5,11    # a0 123, a5 0xed1f00b
    slli    a5,a5,14    # a0 123, a5 0x3b47c02c000
    addi    a5,a5,-8    # a0 123, a5 0x3b47c02bff8
    ld  ra,8(sp)
    or  a0,a0,a5        # a0 0x3b47c02bffb, a5 0x3b47c02bff8
    bseti   a5,zero,32  # a0 0x3b47c02bffb, a5 0x100000000
    addi    a5,a5,-1    # a0 0x3b47c02bffb, a5 0x0ffffffff
    xor a0,a0,a5        # a0 0x3b483fd4004, a5 0x0ffffffff
    bseti   a0,a0,0     # a0 0x3b483fd4005, a5 0x0ffffffff
    addi    sp,sp,16    # sext.w a0,a0 is missing
    jr  ra
main:
    addi    sp,sp,-16
    sd  ra,8(sp)
    call    bar
    li  a5,-2080555008
    addi    a5,a5,5
    bne a0,a5,.L8       # a0 0x3b483fd4005, a5 0x83fd4005
    ld  ra,8(sp)
    li  a0,0
    addi    sp,sp,16
    jr  ra
.L8:
    call    abort

Lin Sinan <mynameisxiaou@gmail.com> 于2023年2月28日周二 13:00写道：

> From: Lin Sinan <sinan.lin@linux.alibaba.com>
>
> The partial subreg check should be for subreg operand(operand 1) instead of
> the immediate operand(operand 2). This change also fix pr68648.c in zbs.
>
> gcc/ChangeLog:
>
>         * config/riscv/bitmanip.md: Fix wrong index in the check.
>
> ---
>  gcc/config/riscv/bitmanip.md | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
> index 14d18edbe62..58a86bd929f 100644
> --- a/gcc/config/riscv/bitmanip.md
> +++ b/gcc/config/riscv/bitmanip.md
> @@ -442,7 +442,7 @@
>         (ior:DI (sign_extend:DI (match_operand:SI 1 "register_operand"
> "r"))
>                 (match_operand 2 "single_bit_mask_operand" "i")))]
>    "TARGET_ZBS && TARGET_64BIT
> -   && !partial_subreg_p (operands[2])"
> +   && !partial_subreg_p (operands[1])"
>    "bseti\t%0,%1,%S2"
>    [(set_attr "type" "bitmanip")])
>
> --
> 2.34.1
>
>